Positive resist composition

ABSTRACT

There is provided a positive resist composition which, during resist pattern formation, can prevent the collapse of very fine resist patterns during the drying step following developing. This positive resist composition is used in a resist pattern formation method comprising a step, within the lithography process, for substituting a liquid remaining on the substrate following alkali developing with a critical drying liquid, and then drying this critical drying liquid by causing passage through a critical state. The positive resist composition comprises a resin component (A), which has an alkali-soluble unit content of less than 20 mol %, contains an acid dissociable, dissolution inhibiting group, and displays increased alkali solubility under action of acid, an acid generator component (B) that generates acid on exposure, and an organic solvent (C) for dissolving the components (A) and (B), and moreover, the component (A) comprises a structural unit (a1) containing an acid dissociable, dissolution inhibiting group, a structural unit (a2) containing a lactone unit, and a structural unit (a3) containing a polycyclic group with an alcoholic hydroxyl group.

TECHNICAL FIELD

The present invention relates to a positive resist composition used in aresist pattern formation method that comprises a critical drying step.

BACKGROUND ART

(Patent Reference 1)

Japanese Unexamined Patent Application, First Publication No. Hei1-220828, page 4, upper right column.

(Patent Reference 2)

Japanese Unexamined Patent Application, First Publication No. Hei9-82629, paragraphs [0024] and [0026].

The patent reference 1 listed above discloses the immersion of asubstrate for which exposure treatment has been completed in asupercritical fluid, thereby achieving a developing effect, a resistremoval effect, and a foreign matter cleaning effect.

The patent reference 2 listed above discloses a method in which thedeveloping solution left following developing treatment, or the rinsesolution left following developing and rinse treatments, is substitutedwith a fluorine-based inert liquid, and the surface of the substrate isthen dried using a nitrogen blower.

The background art relating to the present invention is described below.

Lithography techniques are widely used in the production ofmicrostructures within devices such as semiconductor devices, but asdevice structures have been increasingly miniaturized, demand has alsogrown for the production of finer resist patterns within the lithographyprocess.

Currently, lithography methods can be used in the formation of finepatterns with line widths of no more than 0.20 μm, but recently, demandhas also grown for fine patterns with a large film thickness and anarrow line width, that is, an extremely high so-called aspect ratio(resist height/resist pattern width).

However, these types of fine resist patterns and resist patterns withextremely high aspect ratios tend to be prone to collapse in the stepsfollowing developing treatment.

As a countermeasure to this problem of pattern collapse, a patentreference 3 listed below discloses a method that employs a criticaldrying method, based on the finding that in the drying step followingrinsing, when the liquid surface of the rinse solution trapped withinthe resist pattern falls below the surface of the resist pattern, thesurface tension of the rinse solution applies an attractive force to theresist pattern, thus causing pattern collapse.

In other words, a method is disclosed wherein following formation of aresist film comprising polymethylmethacrylate (PMMA) on a substrate, theresist is exposed with a desired pattern using X-rays, and issubsequently developed in an organic solvent-based developing solutioncomprising a mixture of methyl isobutyl ketone (MIBK) and isopropylalcohol (IPA). The entire substrate is then rinsed with IPA, theresidual IPA left on the substrate is substituted with liquid CO₂, andthis liquid CO₂ then passes through a critical state and converts to agaseous state, meaning no surface tension acts on the resist patternduring the drying process following developing.

(Patent Reference 3)

Japanese Unexamined Patent Application, First Publication No. Hei5-315241, paragraphs [0022] to [0031].

In recent years the development of novel resist materials has progressedsignificantly, and in many cases, an aqueous alkali solution is used asthe developing solution, while pure water is used for the rinsesolution.

However, even if the method disclosed in the above patent reference 3 isapplied to a drying process following developing using an aqueous alkalisolution, all of the moisture trapped within the resist pattern on thesubstrate cannot be removed, and the residual moisture causes surfacetension to act on the resist pattern during the drying step, causingpattern collapse.

Furthermore, even in those cases where the alkali developing solution isrinsed with pure water, moisture form the rinse water causes the sameproblems.

DISCLOSURE OF INVENTION

Accordingly, an object of the present invention is to provide a positiveresist composition, which is used in a resist pattern formation methodthat comprises a critical drying step, and enables the prevention ofresist pattern collapse during a drying step following alkalideveloping.

In order to achieve the above object, a positive resist composition ofthe present invention is a positive resist composition that is used in aresist pattern formation method comprising a step, within thelithography process, for substituting the solution remaining on thesubstrate following alkali developing with a critical drying liquid, andthen drying the critical drying liquid by causing passage through acritical state, wherein the positive resist composition comprises aresin component (A), which has an alkali-soluble unit content of lessthan 20 mol %, contains an acid dissociable, dissolution inhibitinggroup, and displays increased alkali solubility under the action ofacid, an acid generator component (B) that generates acid on exposure,and an organic solvent (C) for dissolving the components (A) and (B),and the component (A) comprises a structural unit (a1) containing anacid dissociable, dissolution inhibiting group, a structural unit (a2)containing a lactone unit, and a structural unit (a3) containing apolycyclic group with an alcoholic hydroxyl group.

The lithography process typically comprises steps for sequentiallyconducting resist application, prebaking, selective exposure, postexposure baking, and alkali developing.

Furthermore, the term “exposure” also includes irradiation with anelectron beam.

By using a positive resist composition of the present invention, thecollapse of very fine resist patterns during the drying step followingdeveloping treatment can be prevented, enabling a resist pattern offavorable shape to be formed with excellent yield.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram describing a drying step according to the presentinvention, in which a resist pattern is dried by causing a criticaldrying liquid to pass through a critical state.

BEST MODE FOR CARRYING OUT THE INVENTION

As follows is a detailed description of the present invention.

[Positive Resist Composition]

A positive resist composition according to the present inventioncomprises a resin component (A), which has an alkali-soluble unitcontent of less than 20 mol %, contains an acid dissociable, dissolutioninhibiting group, and displays increased alkali solubility under theaction of acid, an acid generator component (B) that generates acid onexposure, and an organic solvent (C) for dissolving the components (A)and (B), wherein the component (A) comprises a structural unit (a1)containing an acid dissociable, dissolution inhibiting group, astructural unit (a2) containing a lactone unit, and a structural unit(a3) containing a polycyclic group with an alcoholic hydroxyl group.

In this type of positive resist composition, when acid generated fromthe component (B) acts on the resin, the acid dissociable, dissolutioninhibiting group contained within the component (A) dissociates,converting the entire component (A) from an alkali insoluble state to analkali soluble state.

Accordingly, during resist pattern formation, by selectively irradiatinga positive resist composition applied to a substrate, through a maskpattern, the alkali solubility of the exposed sections improves,enabling alkali developing to be conducted.

Examples of suitable positive resist compositions according to thepresent invention include ArF positive resist compositions that havebeen proposed as favorable materials for exposure methods using ArFexcimer lasers, and KrF positive resist compositions that have beenproposed as favorable materials for exposure methods using KrF excimerlasers, provided the aforementioned alkali-soluble unit content fallswithin the range described above.

The resin component (A) of a KrF positive resist composition typicallycomprises a structural unit derived from hydroxystyrene, and astructural unit derived from a hydroxystyrene in which the hydroxylgroup has been substituted with an acid dissociable, dissolutioninhibiting group, and/or a structural unit derived from a (meth)acrylateester containing an acid dissociable, dissolution inhibiting group.Furthermore, the resin component (A) of a ArF positive resistcomposition typically comprises a resin containing a structural unitderived from a (meth)acrylate ester containing an acid dissociable,dissolution inhibiting group within the principal resin chain.

In the present invention, the term “(meth)acrylate” is a generic termmeaning methacrylate and/or acrylate. A “structural unit” refers to amonomer unit used in producing a polymer.

In the present invention, an alkali-soluble unit refers specifically toa structural unit containing a phenolic hydroxyl group or a carboxylgroup, and includes, for example, structural units derived from ahydroxystyrene shown below in [formula 1], structural units derived froman acrylic acid shown below in [formula 2], and structural units derivedfrom a methacrylic acid shown below in [formula 3]. Alcoholic hydroxylgroups do not form an alkali-soluble unit as defined within the presentinvention.

(wherein, R represents a hydrogen atom or a methyl group)

In the present invention, if the alkali-soluble unit content within thecomponent (A) exceeds 20 mol %, then the resist pattern becomes prone todefects such as surface roughness, thickness loss, and separation fromthe substrate.

The alkali-soluble unit content within the component (A) is preferablyno more than 10 mol %, and even more preferably 5 mol % or less, andmost preferably zero.

[Resin Component (A)]

In a positive resist composition according to the present invention, thecomponent (A) comprises a combination of monomer units with a pluralityof different functions, such as the structural units described below.

A structural unit containing an acid dissociable, dissolution inhibitinggroup (hereafter also referred to as a first structural unit, or (a1)),

a structural unit containing a lactone unit (hereafter also referred toas a second structural unit, or (a2)),

a structural unit containing a polycyclic group with an alcoholichydroxyl group (hereafter also referred to as a third structural unit,or (a3)), and

a structural unit containing a polycyclic group which differs from theacid dissociable, dissolution inhibiting group of the first structuralunit, the lactone unit of the second structural unit, and the alcoholichydroxyl group-containing polycyclic group of the third structural unit(hereafter also referred to as a fourth structural unit, or (a4)).

In the present invention, the term “lactone unit” is a group in whichone hydrogen atom has been removed from a monocyclic or polycycliclactone.

The units (a1) to (a3) are essential, whereas (a4) can be added asdesired, in accordance with the resin characteristics required.

By combining (a1), (a2) and (a3), the solubility resistance relative tothe substitution liquid can be increased, and the etching resistance,resolution, and adhesion between the resist film and the substrate alsoimprove. These three structural units preferably account for at least 80mol %, and even more preferably 90 mol % or greater, of the component(A).

In addition, including the unit (a4) within the component (A) provides aresin with excellent resolution, particularly for isolated patternsthrough to semi dense patterns (line and space patterns in which for aline width of 1, the space width is within a range from 1.2 to 2), andis consequently preferred.

For each of the units (a1) to (a4), a combination of a plurality ofunits may also be used.

[First Structural Unit (a1)]

A first structural unit (a1) of the component (A) may be either astructural unit derived from a (meth)acrylate ester containing an aciddissociable, dissolution inhibiting group, or a structural unit derivedfrom a hydroxystyrene in which the hydroxyl group has been substitutedwith an acid dissociable, dissolution inhibiting group.

There are no particular restrictions on the acid dissociable,dissolution inhibiting group of the unit (a1), provided it displays analkali dissolution inhibiting effect that causes the entire component(A) to be alkali insoluble prior to exposure, but dissociates under theaction of acid generated from the aforementioned component (B) followingexposure, causing the entire component (A) to become alkali soluble.Generally, groups which form a cyclic or chain-like tertiary alkyl esterwith the carboxyl group of (meth)acrylic acid or the hydroxyl group ofhydroxystyrene, tertiary alkoxycarbonyl groups, or chain-likealkoxyalkyl groups are the most widely used.

As the unit (a1), a structural unit derived from a (meth)acrylate ester,and comprising an acid dissociable, dissolution inhibiting groupcontaining a polycyclic group, can be favorably used.

Examples of this polycyclic group include groups in which one hydrogenatom has been removed from a bicycloalkane, a tricycloalkane or atetracycloalkane or the like. Specific examples include groups in whichone hydrogen atom has been removed from a polycycloalkane such asadamantane, norbornane, isobornane, tricyclodecane ortetracyclododecane. These types of polycyclic groups can beappropriately selected from the multitude of groups proposed for usewith ArF resists. Of these groups, adamantyl groups, norbornyl groupsand tetracyclododecanyl groups are preferred in terms of industrialavailability.

Furthermore, as the unit (a1), a structural unit derived fromhydroxystyrene, in which the hydroxyl group has been substituted with anacid dissociable, dissolution inhibiting group, can also be favorablyused.

Ideal monomer units for the first structural unit (a1) are shown belowin [formula 4] through [formula 17].

(wherein, R represents a hydrogen atom or a methyl group, and R¹represents a lower alkyl group)

(wherein, R represents a hydrogen atom or a methyl group, and R² and R³each represent, independently, a lower alkyl group)

(wherein, R represents a hydrogen atom or a methyl group, and R⁴represents a tertiary alkyl group)

(wherein, R represents a hydrogen atom or a methyl group)

(wherein, R represents a hydrogen atom or a methyl group, and R⁵represents a methyl group)

(wherein, R represents a hydrogen atom or a methyl group, and R⁶represents a lower alkyl group)

(wherein, R represents a hydrogen atom or a methyl group)

(wherein, R represents a hydrogen atom or a methyl group)

(wherein, R represents a hydrogen atom or a methyl group, and R⁷represents a lower alkyl group)

(wherein, R represents a hydrogen atom or a methyl group, and R⁸represents a lower alkyl group)

(wherein, R represents a hydrogen atom or a methyl group)

(wherein, R represents a hydrogen atom or a methyl group)

(wherein, R represents a hydrogen atom or a methyl group)

(wherein, R represents a hydrogen atom or a methyl group)

Within the above formulas, the groups R¹ to R³ and R⁶ to R⁸ eachpreferably represent a straight chain or branched lower alkyl group of 1to 5 carbon atoms, and specific examples include a methyl group, ethylgroup, propyl group, isopropyl group, n-butyl group, isobutyl group,tert-butyl group, pentyl group, isopentyl group and neopentyl group.From the viewpoint of industrial availability, a methyl group or anethyl group is preferred.

Furthermore, R⁴ represents a tertiary alkyl group such as a tert-butylgroup or a tert-amyl group, although a tert-butyl group is preferredindustrially.

As the first structural unit (a1), of all the units described above,structural units represented by the general formulas (I), (II) and (III)generate resist patterns following developing treatment that areparticularly resistant to erosion by the substitution liquid used inpost-treatment, and are consequently the most preferred.

[Second Structural Unit (a2)]

A second structural unit (a2) of the component (A) contains a lactoneunit, and is consequently effective in increasing the adhesion betweenthe resist film and the substrate, and improving the affinity with thedeveloping solution.

A unit (a2) of the present invention may be any unit which contains alactone unit and is copolymerizable with the other structural units ofthe component (A).

Examples of suitable monocyclic lactone units include groups in whichone hydrogen atom has been removed from γ-butyrolactone. Furthermore,examples of suitable polycyclic lactones include groups in which onehydrogen atom has been removed from a lactone-containing bicycloalkane.

As the unit (a2), structural units containing a lactone unit, andderived from a (meth)acrylate ester are preferred.

Ideal monomer units for the second structural unit (a2) are shown belowin [formula 18] through [formula 20].

(wherein, R represents a hydrogen atom or a methyl group)

(wherein, R represents a hydrogen atom or a methyl group)

(wherein, R represents a hydrogen atom or a methyl group)

Of the above structural units, γ-butyrolactone esters of (meth)acrylicacid with an ester linkage at the α carbon atom, or norbornane lactoneesters such as those shown in [formula 18] and [formula 19] areparticularly preferred in terms of industrial availability.

[Third Structural Unit (a3)]

Because the hydroxyl group of the alcoholic hydroxyl group-containingpolycyclic group of the third structural unit (a3) of the component (A)is a polar group, use of this unit results in an increased affinity forthe entire component (A) relative to the developing solution, and animprovement in the alkali solubility of the exposed portions.Accordingly, (a3) contributes to an improvement in the resolution.

As the polycyclic group in the unit (a3), any polycyclic group can beappropriately selected from the various polycyclic groups listed in theabove description for the first structural unit (a1).

There are no particular restrictions on the alcoholic hydroxylgroup-containing polycyclic group in the unit (a3), and for example, ahydroxyl group-containing adamantyl group can be favorably used.

In addition, if this hydroxyl group-containing adamantyl group is agroup represented by a general formula (IV) shown below, then it improvethe resist composition in the dry etching resistance improves, and inthe verticalness of the cross-sectional shape of the pattern, both ofwhich are desirable.

(wherein, n represents an integer from 1 to 3)

The third structural unit (a3) may be any unit which contains anaforementioned alcoholic hydroxyl group-containing polycyclic group, andis copolymerizable with the other structural units of the component (A).

Structural units derived from (meth)acrylate esters are particularlypreferred.

Specifically, structural units represented by a general formula (IVa)shown below are preferred.

(wherein, R represents a hydrogen atom or a methyl group)[Fourth Structural Unit (a4)]

In a unit (a4), a polycyclic group which “differs from the aciddissociable, dissolution inhibiting group, the lactone unit, and thealcoholic hydroxyl group-containing polycyclic group” means that in thecomponent (A), the polycyclic group of the structural unit (a4) is apolycyclic group which does not duplicate the acid dissociable,dissolution inhibiting group of the first structural unit (a1), thelactone unit of the second structural unit (a2), or the alcoholichydroxyl group-containing polycyclic group of the third structural unit(a3), and also means that the unit (a4) does not have the aciddissociable, dissolution inhibiting group of the first structural unit,the lactone unit of the second structural unit, or the alcoholichydroxyl group containing polycyclic group of the third structural unit,which constitute the component (A).

There are no particular restrictions on the polycyclic group of the unit(a4), provided it is selected so as not to duplicate any of thestructural units used in the units (a1) to (a3) of a single component(A). For example, as the polycyclic group in the unit (a4), aliphaticpolycyclic groups like those listed in the above description for thestructural unit (a1) can be used, and any of the multitude of materialsconventionally used for ArF positive resist materials can be used.

From the viewpoint of industrial availability, one or more groupsselected from amongst tricyclodecanyl groups, adamantyl groups ortetracyclododecanyl groups is preferred.

The unit (a4) may be any unit which contains an aforementionedpolycyclic group, and is copolymerizable with the other structural unitsof the component (A).

Preferred examples of (a4) are shown below in [formula 23] through[formula 25].

(wherein, R represents a hydrogen atom or a methyl group)

(wherein, R represents a hydrogen atom or a methyl group)

(wherein, R represents a hydrogen atom or a methyl group)

In the present invention, component (A) compositions in which the firststructural unit (a1) accounts for 20 to 60 mol %, and preferably from 30to 50 mol %, of the combined total of all the structural units of thecomponent (A) display excellent resolution, and are consequentlypreferred.

Furthermore, compositions in which the second structural unit (a2)accounts for 20 to 60 mol %, and preferably from 30 to 50 mol %, of thecombined total of all the structural units of the component (A) displayexcellent resolution, and are consequently preferred.

Furthermore, compositions in which the third structural unit (a3)accounts for 5 to 50 mol %, and preferably from 10 to 40 mol %, of thecombined total of all the structural units of the component (A) displayexcellent resist pattern shape, and are consequently preferred.

In those cases where the fourth structural unit (a4) is used,compositions in which the unit (a4) accounts for 1 to 30 mol %, andpreferably from 5 to 20 mol %, of the combined total of all thestructural units of the component (A) offer superior resolution forisolated patterns through to semi-dense patterns, and are consequentlypreferred.

Furthermore, there are no particular restrictions on the weight averagemolecular weight (the polystyrene equivalent value, this also applies tosubsequent molecular weight values) of the component (A), althoughvalues are typically within a range from 5,000 to 30,000, and preferablyfrom 8,000 to 20,000. If the molecular weight is greater than thisrange, then the solubility of the component in the resist solventdeteriorates, whereas if the molecular weight is too small, there is adanger of a deterioration in the cross sectional shape of the resistpattern.

The resin component (A) in the present invention can be produced easilyby a conventional radical polymerization of monomers corresponding withthe structural units (a1), (a2), (a3), and where required (a4), using aradical polymerization initiator such as azobisisobutyronitrile (AIBN).The resin component (A) preferably comprises at least one unit selectedfrom the above general formulas (I) through (III) as the structural unit(a1).

Furthermore, in order to ensure that the alkali-soluble unit contentwithin the component (A) is less than 20 mol %, the proportion ofmonomers containing alkali-soluble units within the combination of allthe monomers subjected to copolymerization should be restricted to lessthan 20 mol %.

[Acid Generator Component (B)]

In the present invention, as the acid generator component (B), acompound appropriately selected from known materials used as acidgenerators in conventional chemically amplified resists can be used.

Examples of suitable acid generators include onium salts such asdiphenyliodonium trifluoromethanesulfonate,(4-methoxyphenyl)phenyliodonium trifluoromethanesulfonate,bis(p-tert-butylphenyl)iodonium trifluoromethanesulfonate,triphenylsulfonium trifluoromethanesulfonate,(4-methoxyphenyl)diphenylsulfonium trifluoromethanesulfonate,(4-methylphenyl)diphenylsulfonium nonafluorobutanesulfonate,(p-tert-butylphenyl)diphenylsulfonium trifluoromethanesulfonate,diphenyliodonium nonafluorobutanesulfonate,bis(p-tert-butylphenyl)iodonium nonafluorobutanesulfonate, andtriphenylsulfonium nonafluorobutanesulfonate. Of these, onium salts witha fluorinated alkylsulfonate ion as the anion are particularlypreferred.

As this component (B), either a single acid generator or a combinationof two or more acid generators may be used.

The quantity used of the component (B) is typically within a range from0.5 to 30 parts by weight, and preferably from 1 to 10 parts by weight,per 100 parts by weight of the component (A). At quantities less than0.5 parts by weight, pattern formation does not proceed satisfactorily,whereas if the quantity exceeds 30 parts by weight, achieving a uniformsolution becomes difficult, and there is a danger of a deterioration inthe storage stability.

[Organic Solvent (C)]

A positive resist composition according to the present invention can beproduced by dissolving the component (A) and the component (B), togetherwith any optional components (D) described below, in an organic solvent(C).

The organic solvent (C) may be any solvent capable of dissolving thecomponent (A) and the component (B) to generate a uniform solution, andone or more solvents selected from known materials used as the solventsfor conventional chemically amplified resists can be used.

Specific examples of the solvent include ketones such as acetone, methylethyl ketone, cyclohexanone, methyl isoamyl ketone and 2-heptanone;polyhydric alcohols and derivatives thereof such as ethylene glycol,ethylene glycol monoacetate, diethylene glycol, diethylene glycolmonoacetate, propylene glycol, propylene glycol monoacetate, dipropyleneglycol, or the monomethyl ether, monoethyl ether, monopropyl ether,monobutyl ether or monophenyl ether of dipropylene glycol monoacetate;cyclic ethers such as dioxane; and esters such as methyl lactate, ethyllactate, methyl acetate, ethyl acetate, butyl acetate, methylpyruvate,ethyl pyruvate, methyl methoxypropionate, and ethyl ethoxypropionate.These organic solvents can be used alone, or as a mixed solvent of twoor more different solvents.

In particular, mixed solvents of propylene glycol monomethyl etheracetate (PGMEA) and a polar solvent containing a hydroxyl group or alactone such as propylene glycol monomethyl ether (PGME), ethyl lactate(EL) or γ-butyrolactone offer improved storage stability for positiveresist compositions, and are consequently preferred. In cases in whichEL is mixed with PGMEA, the weight ratio of PGMEA:EL is preferablywithin a range from 6:4 to 4:6.

In cases where PGME is mixed with PGMEA, the weight ratio of PGMEA:PGMEis typically within a range from 8:2 to 2:8, and preferably from 8:2 to5:5.

Mixed solvents of PGMEA and PGME improve the storage stability ofpositive resist compositions, particularly in those cases where acomponent (A) comprising all of the units (a1) through (a4) is used, andare consequently preferred.

In addition, mixed solvents containing at least one of PGMEA and ethyllactate, together with γ-butyrolactone are also preferred as the organicsolvent (C). In such cases, the weight ratio of the former and lattercomponents in the mixed solvent is preferably within a range from 70:30to 95:5.

In a positive resist composition according to the present invention,there are no particular restrictions on the quantity of the component(C), although typically, a sufficient quantity of the component (C) isadded to produce a solid fraction concentration within the resistcomposition of 3 to 30% by weight, with the actual value set inaccordance with the resist film thickness.

[Other Components]

Furthermore, in a positive resist composition of the present invention,in order to improve the resist pattern shape and the long term stability(the post exposure stability of the latent image formed by thepattern-wise exposure of the resist layer), a secondary lower aliphaticamine or a tertiary lower aliphatic amine can also be added as anoptional component (D).

Here, a lower aliphatic amine refers to an alkyl or alkyl alcohol amineof no more than 5 carbon atoms, and examples of these secondary andtertiary amines include trimethylamine, diethylamine, triethylamine,di-n-propylamine, tri-n-propylamine, tripentylamine, diethanolamine andtriethanolamine, and of these, alkanolamines such as triethanolamine arepreferred.

These may be used alone, or in combinations of two or more differentcompounds.

These types of amines are typically added in quantities within a rangefrom 0.01 to 2.0% by weight relative to the quantity of the component(A).

Other miscible additives can also be added to a positive type resistcomposition of the present invention according to need, includingadditive resins for improving the properties of the resist film,surfactants for improving the ease of application, dissolutioninhibitors, plasticizers, stabilizers, colorants and halation preventionagents.

[Pattern Formation Method]

Next is a description of a pattern formation method according to thepresent invention.

First, a positive resist composition according to the present inventionis applied to the top of a substrate such as a silicon wafer using aspinner or the like, and a prebake is then performed. The coating of thepositive resist composition is then selectively exposed using anexposure apparatus, and is then subjected to PEB (post exposure baking).The term “selective exposure” includes both exposure through a maskpattern with an exposure light source, as described below, as well asirradiation through a mask pattern with an electron beam, and electronbeam lithography without using a mask pattern. Subsequently, developingis conducted using an alkali developing liquid comprising an aqueousalkali solution, and the resist is then rinsed with pure water. Thiswater rinsing step involves dripping or spraying water onto thesubstrate surface while rotating the substrate, thereby washing thedeveloping solution, and the resist composition dissolved within thedeveloping solution, off the substrate. In this manner, the coating ofthe positive resist composition is patterned into a shape that matchesthe mask pattern, yielding a wet resist pattern.

The steps up until this point can be conducted using conventionaltechniques. The operating conditions are preferably set in accordancewith the makeup and the characteristics of the positive resistcomposition being used.

There are no particular restrictions on the wavelength used for theexposure, and a radiation such as an ArF excimer laser, a KrF excimerlaser, a F₂ laser, EUV (extreme ultraviolet), VUV (vacuum ultraviolet),electron beam, X-ray or soft X-ray radiation can be used. The positiveresist composition according to the present invention is particularlyuseful for KrF excimer lasers, ArF excimer lasers, and electron beams.

An organic or inorganic anti-reflective film may also be providedbetween the substrate and the applied coating of the resist composition.

The water rinsing step following the developing treatment can beomitted, but incorporating the water rinsing step to wash the alkalicomponents of the alkali developing solution off the substrate ispreferred. The description below focuses on an embodiment in which thewater rinsing step is included.

Following water rinsing, the substrate is supplied to the subsequentsubstitution step with the undried resist pattern still immersed in purewater.

In the substitution step, an operation for substituting the liquid onthe substrate, which is water in the case of this embodiment, isconducted either once or a plurality of times, so that the undriedresist pattern is converted to a state of immersion within thesubstitution liquid. There are no particular restrictions on theoperation used for substituting the liquid on the substrate with thesubstitution liquid, and suitable methods include immersing thesubstrate within the substitution liquid, and spraying the substratewith the substitution liquid.

Furthermore, in this substitution step, the liquid on the substrate mayfirst be substituted with a first substitution liquid, and this firstsubstitution liquid then substituted with a second substitution liquid,so that the undried resist pattern on the substrate is completelyimmersed within the second substitution liquid.

In this substitution step following water rinsing, the operation forsubstituting the liquid on the substrate with the substitution liquid ispreferably conducted at least 2 times, thereby enabling a highlyeffective removal of the original liquid from the substrate.

As the substitution liquid of the present invention, any material can beused provided it is an inert liquid that does not react with the undriedresist pattern, is capable of substituting the liquid present on thesubstrate, and is able to be substituted by a critical drying liquid ofthe present invention. Substitution liquids containing a surfactant areable to more efficiently replace the liquid on the substrate, and areconsequently preferred.

Fluorine-based inert liquids can be favorably employed as thesubstitution liquid. Specific examples of such fluorine-based inertliquids include liquids comprising, as a principal component, afluorine-based compound such as C₃HCl₂F₅, C₄F₉OCH₃, C₄F₉OC₂H₅, C₅H₃F₇,C₅H₂F₁₀, and C₂H₃Cl₂F. Fluorine-based inert liquids comprising one ormore of these fluorine-based compounds mixed with an alcohol such asisopropyl alcohol, methanol, or ethanol are also preferred.

Furthermore, in those cases where, as described above, substitution isconducted in two stages using a first substitution liquid and a secondsubstitution liquid, by using a liquid containing an added surfactant asthe first substitution liquid, and a liquid containing no surfactant asthe second substitution liquid, all traces of residual surfactant can beremoved from the substrate surface by completion of the substitutionstep, which is desirable.

Using a liquid containing an added surfactant as the first substitutionliquid is effective in those cases where a very fine pattern is formed,and particularly when a very fine pattern is formed using electron beamexposure.

Following the substitution step, the undried resist pattern iscompletely immersed within the substitution liquid, and the substrate issupplied to the subsequent drying step in this state.

In the drying step, first, the substitution liquid on the substrate issubstituted with a critical drying liquid. The critical drying liquidcan use a fluid that is capable of adopting a liquid phase duringsubstitution of the substitution liquid, such as carbon dioxide, whichis a gaseous fluid under normal temperature and pressure conditions, butcan be liquefied by suitably adjusting the temperature and pressure ofthe substitution atmosphere.

As the critical drying liquid, fluids for which the critical temperatureis at least 0° C. and the critical pressure is no more than 30 MPa canbe favorably used. Specific examples include CO₂, H₂O, C₃H₆, N₂O, andCHF₃. The critical temperature (hereafter also referred to as Tc) andcritical pressure (hereafter also referred to as Pc) for each of thesefluids are shown below.

CO₂: Tc=31.1° C., Pc=approximately 7.38 MPa (72.8 atm.)

H₂O: Tc=374° C., Pc=approximately 22.0 MPa (217.6 atm.)

C₃H₆: Tc=92.3° C., Pc=approximately 4.6 MPa (45.6 atm.)

N₂O: Tc=36.5° C., Pc=approximately 7.27 MPa (71.7 atm.)

CHF₃: Tc=25.9° C., Pc=approximately 48.4 MPa (47.8 atm.)

Of these, carbon dioxide is preferred in terms of the conditionsrequired for industrial application.

The description below focuses on an example in which liquid CO₂ is usedas the critical drying liquid.

FIG. 1 is a diagram showing a schematic illustration of the gas-liquidequilibrium curve for a fluid. In the FIGURE, the point A marks thecritical point, and in the case of carbon dioxide, this point occurs atTc=31.1° C., and Pc=7.38 MPa.

There are no particular restrictions on the method used for substitutingthe substitution liquid on the substrate with the critical dryingliquid, although in those cases where liquid CO₂ is used, followingcompletion of the substitution step, the substrate, which comprises aresist pattern immersed within the substitution liquid, is placed insidea pressure vessel, the interior of which is capable of beingpressurized. At this point, the temperature and pressure inside thepressure vessel are set to normal levels, namely, room temperature andatmospheric pressure (point (1) in FIG. 1). Subsequently, liquid CO₂ isfed into the vessel, while the temperature and pressure inside thevessel are adjusted to conditions under which CO₂ remains in the liquidphase (for example, point (2) in FIG. 1), and the inside of the pressurevessel is filled with liquid CO₂. With the temperature and pressureinside the pressure vessel maintained, the supply of liquid CO₂ iscontinued, so that the liquid CO₂ that has mixed with the substitutionliquid flows out of the pressure vessel, thereby substituting thesubstitution liquid on the surface of the substrate with a criticaldrying liquid (liquid CO₂).

The critical drying liquid is then dried by passage through the criticalstate. Specifically, the inside of the pressure vessel is adjusted to atemperature and pressure that causes the critical drying liquid to reacha supercritical state (for example, point (3) in FIG. 1), and with thattemperature maintained, the supercritical state critical drying liquidis then expelled from the pressure vessel. This causes the pressure ofthe critical drying liquid to fall, reaching a temperature and pressureshown by a point (4) for example, and the liquid on the substrate isthen removed in a gaseous state, leaving the substrate dry. If required,the inside of the pressure vessel can then be cooled to roomtemperature.

In those cases where liquid CO₂ is used as the critical drying liquid,the substitution liquid on the substrate is replaced with liquid CO₂,and the inside of the pressure vessel is then adjusted to a temperatureof at least 31.1° C., and a pressure of at least 7.38 MPa, therebyplacing the CO₂ in a supercritical state. Subsequently, with thetemperature maintained at 31.1° C. or higher, the CO₂ is allowed togradually leak from the vessel, and once the pressure inside thepressure vessel falls below 7.38 MPa, and finally reaches atmosphericpressure. This causes the supercritical state CO₂ to convert to the gasphase, leaving the substrate in a dry state. Completing the drying stepby cooling the temperature inside the pressure vessel to roomtemperature enables a dried resist pattern to be obtained.

When converting the critical drying liquid to a critical state,achieving a supercritical state by raising the temperature above thecritical temperature and raising the pressure above the criticalpressure is preferred, although even in a subcritical state, where theliquid is close to a supercritical state, but the temperature is lessthan the critical temperature and/or the pressure is less than thecritical pressure, the liquid can still be effectively removed from thesubstrate.

By forming a resist pattern in this manner, collapse of the resistpattern during the drying step can be prevented, even for resistpatterns with very small line widths, resist patterns with shapes thatare prone to collapse, such as resist patterns with high aspect ratios,and line and space patterns with a small pitch, which have beenparticularly prone to pattern collapse.

In this description, the pitch of a line and space pattern is thecombined distance of a resist pattern width and a space width in adirection across the width of the pattern lines.

Furthermore, even in cases where the water rinsing step is omitted, thesame substitution and drying steps can be applied to the drying of thedeveloping solution (aqueous alkali solution) from the surface of thedeveloped substrate, and this enables prevention of the collapse of theresist pattern.

In addition, because the resist pattern is formed from a resistcomposition comprising a resin component (A) containing the abovestructural units (a1), (a2), and (a3), with an alkali-soluble unitcontent of less than 20 mol %, even when the undried resist pattern isbrought into contact with a substitution liquid, defects such as surfaceroughening, thickness loss, and separation from the substrate do notoccur, meaning a resist pattern with good shape precision can beobtained in high yield.

A resist pattern formed using a method according to the presentinvention is preferably a high density line and space pattern with aline width within a range from 20 to 130 nm, and preferably from 30 to100 nm, an aspect ratio within a range from 2.0 to 10.0, and preferablyfrom 2.5 to 8.0, and a pitch within a range from 40 to 300 nm, andpreferably from 50 to 260 nm.

If the line width exceeds the above range, then formation of the resistpattern can be conducted using a conventional method, without relying onthe method according to the present invention, whereas if the line widthis smaller than the above range, then pattern formation becomesdifficult.

If the aspect ratio is smaller than the above range, then formation ofthe resist pattern can be conducted using a conventional method, withoutrelying on the method according to the present invention, whereas if theaspect ratio exceeds the above range, then pattern formation becomesdifficult.

If the pitch exceeds the above range, then formation of the resistpattern can be conducted using a conventional method, without relying onthe method according to the present invention, whereas if the pitch issmaller than the above range, then pattern formation becomes difficult.

Furthermore, by employing a critical drying step, and also usingelectron beam exposure, particularly fine resist patterns, and resistpatterns with very high aspect ratios can be achieved. For example, evena very fine line and space pattern with a line width within a range from20 to 100 nm, and preferably from 20 to 80 nm, and an aspect ratiowithin a range from 2.0 to 10.0 can be formed without pattern collapse.

EXAMPLES

As follows is a more detailed description of the present invention,based on a series of examples.

Example 1

A component (A), a component (B) and a component (D) described belowwere dissolved uniformly in a component (C), yielding a positive resistcomposition.

As the component (A), 100 parts by weight of an acrylate ester-basedcopolymer comprising the three structural units shown in [formula 26]was used. The proportions p, q and r of each of the structural unitsused in preparing the component (A) were p=40 mol %, q=40 mol % and r=20mol % respectively.

The alkali-soluble unit content within the thus prepared component (A)was 0 mol %, and the weight average molecular weight of the component(A) was 10,000.

As the component (B), 2.0 parts by weight of triphenylsulfoniumnonafluorobutanesulfonate and 0.6 parts by weight of triphenylsulfoniumtrifluoromethanesulfonate were used.

As the component (C), a mixed solvent of 450 parts by weight ofpropylene glycol monomethyl ether acetate and 300 parts by weight ofethyl lactate was used.

As the component (D), 0.3 parts by weight of triethanolamine was used.

Subsequently, the prepared positive resist composition was applied tothe surface of a silicon wafer using a spinner, and was then prebakedand dried on a hot plate at 130° C. for 90 seconds, thus forming aresist layer with a film thickness of 340 nm.

Next, this layer was selectively irradiated with an ArF excimer laser(193 nm) through a phase shift mask, using an ArF exposure apparatusS-302 (manufactured by Nikon Corporation, (NA (numerical aperture)=0.60,σ=0.40).

A PEB treatment was then performed at 130° C. for 90 seconds, and theresist layer was then subjected to puddle development in an alkalideveloping solution, for 60 seconds at 23° C. The substrate was thenrinsed with pure water for 180 seconds. As the alkali developingsolution, a 2.38% by weight aqueous solution of tetramethylammoniumhydroxide was used.

The rinsed substrate was immersed in a first substitution liquid, andfollowing replacement of the liquid on the substrate with this firstsubstitution liquid, the substrate was immersed in a second substitutionliquid, thereby replacing the liquid on the substrate with this secondsubstitution liquid. As the first substitution liquid, a fluorine-basedinert liquid comprising CF₃CF₂CHCl₂ and CClF₂CF₂CHClF as primarycomponents, and also containing a surfactant (brand name: AK225DW,manufactured by Asahi Glass Co., Ltd.) was used, and as the secondsubstitution liquid, a product AK225 manufactured by Asahi Glass Co.,Ltd, containing only the above fluorine-based inert compounds as primarycomponents, was used. These liquids are marketed as cleaning agents foruse on members formed from metal, plastics, or rubbers.

Subsequently, the substrate was subjected to critical drying using amicrostructure drying device (SRD-2020, manufactured by Hitachi ScienceSystems, Ltd.).

In other words, the substrate was first placed inside a pressure vessel.At this point, the temperature inside the pressure vessel was roomtemperature (23° C.) and the pressure was atmospheric pressure (thepoint (1) in FIG. 1).

Subsequently, liquid CO₂ was fed into the vessel, while the pressureinside the vessel was raised to 7.5 MPa. The temperature was held at 23°C. (the point (2) in FIG. 1). With the temperature and pressuremaintained inside the pressure vessel, liquid CO₂ was suppliedcontinuously to the pressure vessel, so that the liquid CO₂ inside thepressure vessel was caused to flow out of the vessel, therebysubstituting the substitution liquid on the surface of the substratewith a critical drying liquid.

Subsequently, with the pressure inside the pressure vessel maintained at7.5 MPa, the temperature was raised to 35° C. at a rate of temperatureincrease of 2° C./minute, thereby placing the CO₂ inside the pressurevessel in a supercritical state (the point (3) in FIG. 1).

With the temperature maintained at 35° C. or higher, the CO₂ was allowedto gradually leak from the vessel. This caused the pressure inside thepressure vessel to gradually fall to atmospheric pressure, therebyconverting the CO₂ to a gaseous state (the point (4) in FIG. 1).

The temperature inside the pressure vessel was then lowered to roomtemperature, completing the drying process.

The thus dried substrate comprised a line and space pattern with a linewidth of 90 nm, an aspect ratio of 3.8, and a pitch of 180 nm, which hadbeen formed with a favorable shape, and with no pattern collapse.

Comparative Example 1

The process of the example 1 was repeated up to and including the waterrinsing step, and the substrate was then subjected to spin drying byrotating the substrate, and then heating on a hot plate at 100° C. toremove any residual pure water.

The thus dried substrate displayed a resist pattern of favorable shape,but adjacent patterns had leaned towards one another.

Example 2

When the process of the example 1 was repeated, and the exposure dosewas increased (overdose) to form an even finer resist pattern, a lineand space pattern with a line width of 48 nm, an aspect ratio of 7.1,and a pitch of 180 nm was formed. The shape of the resist pattern wasfavorable, and no pattern collapse had occurred.

Comparative Example 2

With the exception of altering the component (A) to 100 parts by weightof a resin in which the proportions of the three structural units shownin [formula 26] had been altered to p=30 mol %, q=30 mol % and r=10 mol% respectively, and an additional 30 mol % of a structural unitrepresented by the [formula 3] had been incorporated, a resistcomposition was prepared in the same manner as the example 1.

When the thus obtained resist composition was used to form a resistpattern in the same manner as the example 1, a line and space patternwith a line width of 90 nm and a pitch of 180 nm was obtained, but whenthis line and space pattern was immersed in the first substitutionliquid, surface roughening, thickness loss, and separation form thesubstrate all occurred, leaving a very poor pattern shape.

Example 3

As the component (A), the same copolymer as the example 1 was used.

As the component (B), 6.82 parts by weight of triphenylsulfoniumnonafluorobutanesulfonate was used.

As the component (C), a mixed solvent of 450 parts by weight ofpropylene glycol monomethyl ether acetate and 300 parts by weight ofpropylene glycol monomethyl ether was used.

As the component (D), 0.3 parts by weight of triethanolamine was used.

The component (A), the component (B), the component (D), and 0.05 partsby weight of a non-ionic fluorine/silicone-based surfactant (brand name:Megafac R-08 (manufactured by Dainippon Ink and Chemicals,Incorporated)) were dissolved uniformly in the component (C), thusyielding a positive resist composition.

Subsequently, the thus obtained positive resist composition was appliedto the surface of a hexamethyldisilazane-treated silicon wafer using aspinner, and was then prebaked and dried on a hot plate at 150° C. for90 seconds, thus forming a resist layer with a film thickness of 340 nm.

Next, this layer was selectively exposed using an electron beamlithography apparatus (HL-800D, manufactured by Hitachi, Ltd.,accelerating voltage 70 kV), using a method in which the pattern wasformed by direct irradiation of the electron beam onto the photoresistlayer.

A PEB treatment was then performed at 140° C. for 90 seconds, and theresist layer was then subjected to dipping development in an alkalideveloping solution, for 60 seconds at 23° C. The substrate was thenrinsed with pure water for 60 seconds. As the alkali developingsolution, a 2.38% by weight aqueous solution of tetramethylammoniumhydroxide was used.

The rinsed substrate was immersed in a first substitution liquid for 60seconds, and following replacement of the liquid on the substrate withthis first substitution liquid, the substrate was immersed in a secondsubstitution liquid for 60 seconds, thereby replacing the liquid on thesubstrate with this second substitution liquid. The first and secondsubstitution liquids used the same products AK225DW and AK225 as thoseused in the example 1.

The substrate was then subjected to critical drying using amicrostructure drying device in the same manner as the example 1.

The thus dried substrate comprised a line and space pattern with a linewidth of 70 nm, an aspect ratio of 4.86, and a pitch of 140 nm, whichhad been formed with a favorable shape, and with no pattern collapse.

Example 4

With the exception of altering the first substitution liquid to aproduct AK225DH, manufactured by Asahi Glass Co., Ltd., comprisingCF₃CF₂CHCl₂ and CClF₂CF₂CHClF as primary components, and also containinga surfactant, a resist pattern was formed in the same manner as theexample 3. A line and space pattern with a line width of 70 nm, anaspect ratio of 4.86, and a pitch of 140 nm was formed on the substrate,with a favorable pattern shape and no pattern collapse.

INDUSTRIAL APPLICABILITY

As described above, according to the present invention, the collapse ofvery fine resist patterns during the drying step following developingtreatment can be prevented, and a resist pattern of favorable shape canbe formed with excellent yield, which is industrially extremely useful.

1. A positive resist composition that is used in a resist patternformation method comprising a step, within a lithography process, forsubstituting a liquid remaining on a substrate following alkalideveloping with a critical drying liquid, and then drying said criticaldrying liquid by causing passage through a critical state, wherein saidpositive resist composition comprises a resin component (A), which hasan alkali-soluble unit content of less than 20 mol %, contains an aciddissociable, dissolution inhibiting group, and displays increased alkalisolubility under action of acid, an acid generator component (B) thatgenerates acid on exposure, and an organic solvent (C) for dissolvingsaid components (A) and (B), and said component (A) comprises astructural unit (a1) containing an acid dissociable, dissolutioninhibiting group, a structural unit (a2) containing a lactone unit, anda structural unit (a3) containing a polycyclic group with an alcoholichydroxyl group.
 2. A positive resist composition according to claim 1,wherein said alkali-soluble unit is at least one unit selected from agroup consisting of structural units containing a phenolic hydroxylgroup, and structural units containing a carboxyl group.
 3. A positiveresist composition according to claim 1, wherein quantities of saidstructural units (a1) to (a3) within said component (A) are from 20 to60 mol % for said (a1), from 20 to 60 mol % for said (a2), and from 5 to50 mol % for said (a3), and said alkali-soluble unit content is zero. 4.A positive resist composition according to claim 1, wherein saidcomponent (A) further comprises a structural unit (a4) containing apolycyclic group that differs from said acid dissociable, dissolutioninhibiting group, said lactone unit, and said polycyclic group with analcoholic hydroxyl group.
 5. A positive resist composition according toclaim 4, wherein quantities of said structural units (a1) to (a4) withinsaid component (A) are from 20 to 60 mol % for said (a1), from 20 to 60mol % for said (a2), from 5 to 50 mol % for said (a3), and from 1 to 30mol % for said (a4), and said alkali-soluble unit content is zero.
 6. Apositive resist composition according to claim 1, wherein said component(B) is an onium salt with a fluorinated alkylsulfonate ion as an anion.7. A positive resist composition according to claim 1, furthercomprising a secondary or tertiary lower aliphatic amine (D) in aquantity within a range from 0.01 to 2.0% by weight relative to saidcomponent (A).
 8. A positive resist composition comprising: a resincomponent (A) that displays increased alkali solubility under action ofacid, comprising: a structural unit (a1) containing an acid dissociable,dissolution inhibiting group, a structural unit (a2) containing alactone unit, a structural unit (a3) containing a polycyclic group withan alcoholic hydroxyl group, and an alkali-soluble unit of less than 20mol %; an acid generator component (B) that generates acid on exposure;and an organic solvent (C) for dissolving said components (A) and (B).9. The positive resist composition according to claim 8, wherein saidalkali-soluble unit includes at least one unit selected from a groupconsisting of structural units containing a phenolic hydroxyl group, andstructural units containing a carboxyl group, but does not includealcoholic hydroxyl groups.
 10. The positive resist composition accordingto claim 8, wherein the structural units (a1), (a2), and (a3) arecontained in the component (A) in an amount of from 20-60 mol %, from20-60 mol %, and from 5-50 mol %, respectively, and no alkali-solubleunit is contained.
 11. The positive resist composition according toclaim 10, wherein the component (A) further comprises 1-30 mol % of astructural unit (a4) containing a polycyclic group that differs from theacid dissociable, dissolution inhibiting group, the lactone unit, andthe polycyclic group with an alcoholic hydroxyl group.
 12. The positiveresist composition according to claim 8, wherein the acid dissociable,dissolution inhibiting group of the structural unit (a1) is a groupwhich forms a cyclic or chain-like tertiary alkyl ester with thecarboxyl group of (meth)acrylic acid or the hydroxyl group ofhydroxystyrene; a tertiary alkoxycarbonyl group; or a chain-likealkoxyalkyl group.
 13. The positive resist composition according toclaim 8, wherein the component (B) is an onium salt with a fluorinatedalkylsulfonate ion as an anion.
 14. The positive resist compositionaccording to claim 13, wherein the component (B) is contained in a rangeof from 0.5 to 30 parts by weight per 100 parts of the component (A).15. A method of forming a resist pattern comprising a lithographyprocess comprising: forming and exposing a resist layer on a substrateusing the resist pattern composition of claim 8; conducting alkalideveloping of the exposed resist layer to form a resist pattern;substituting a solution remaining on the substrate with a criticaldrying liquid; and drying the critical drying liquid through itscritical state.